Gueuze beers are prepared by mixing young and old lambic beers and are bottle refermented
spontaneously for aging. The present study analysed the microbiota and
metabolites present in gueuze beers that were aged between a few months and up to 17
years. Yeasts were cultivated from all beers sampled, but bacteria could not be grown from
beers older than 5 years. Lactic acid and ethyl lactate concentrations increased steadily
during aging, whereas ethanol concentrations remained constant. The concentrations of
isoamyl acetate and ethyl decanoate decreased during the aging process. Hence, ethyl
lactate and ethyl decanoate can be considered as positive and negative gueuze beer-aging
metabolite biomarkers respectively. Nevertheless, considerable bottle-to-bottle variation in
the metabolite profiles was found, which hindered the generalisation of the effects seen
during the aging of the gueuze beers examined, but which illustrated the unique character
of the lambic beers. The present results further indicate that gueuze beers are preferably
aged for less than 10 years.